C :: Converting Decimal Number To Any Base Then Find Ones And Twos Complement

I have the code working on converting a decimal number to base 1 through 16. I need getting the code to output the one's and two's complement.

Code:
#include <stdio.h>
int main(void) {
char base_digits[16] =
{'0', '1', '2', '3', '4', '5', '6', '7',
'8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};

int converted_number[64];
long int number_to_convert;
int next_digit, base, index=0, a;

/* get the number and base */

[Code] ....